Add in testing for two text() examples

Note - The PNG are not correct yet (not generating properly on GCC
4.8?).
Temp workaround for #514 - Compile OpenSCAD and CGAL with gcc/g++ 4.7 (if 4.8 found)
Fixed up test images for example025 and 26
Temp - Hack to allow easy building of openscad_nogui with gcc-4.7
Add expected results for dumptests example025 and 26